Problem with exporting FBX file with multiple materials and UV Maps
I was trying to export FBX and said error was poping up. It was 3 objects with 3 different UV maps on one MAP ( i think its called UV Atlas). 3 materials all assigned even had vertex group for each one. After multiple trys i separated all of the objects and started exporting them one by one. It appears UV map on one of them wouldnt let the whole model to export. I tried with materials as i heard that un assigned materials can prevent you from exporting... i tried saving to obj and than back to fbx still nothing. I made new seams (cause i found in error info multiple UVIndex mentions) and unwrapped it once more and it exported. Simply as that.